5.56×45mm NATO
The 5.56 x 45 mm NATO (5.56, 5.56x45mm, or 5.56 NATO) cartridge is one of the standardized cartridges for the nations in the NATO organization. It is approximately .224 inches in diameter. Design details The 5.56 NATO cartridge is visually nearly identical to the .223 Remington cartridge, with the exception of the casing headstamp, which usually bears the NATO insignia. It can be fired in some of the same weapons. The 5.56 can use the same projectiles as .223, as well as projectiles developed specifically for 5.56. The cartridge is loaded to a pressure that would be considered excessive in a .223 chamber, however - the .223 chamber has a shorter and sharper leade compared to the 5.56 chamber, as well as less effective freebore. Firing this cartridge in a .223 chamber will cause the pressure to spike due to the projectile engaging the rifling sooner than it would in a 5.56 chamber. Use caution when firing 5.56 NATO cartridges in a weapon suspected to have a .223 chamber; common symptoms are popped primers and gas staining on the primers. Contrary to popular belief, the 5.56 NATO brass cases do not have significantly reduced case capacity due to the thickness of the case; there is no discernible difference, though the capacity will vary slightly due to manufacturing tolerances. The M193 projectile will fragment reliably so long as its flight velocity remains at or above 2700 feet per second; the M855 projectile will fragment reliably above 2500 feet per second. Variations The 5.56x45mm NATO has several variations and designations, both military and non-military. M193 This cartridge has a full metal jacket 55-grain projectile. The bullet does not bear any special markings. This cartridge is loaded to a pressure of 52,000 psi. M196 This cartridge is a tracer. Its tip is painted red. M197 This cartridge has the same projectile as the M193; however, this is a proof round, loaded to very high pressures to conduct high pressure tests (HPT) on barrels and bolts. This round is loaded to a pressure of 70,000 psi. M199 This cartridge is a dummy round. It is marked by several indentations in the bullet. There is no primer, and no propellant is loaded. M200 This cartridge is a blank. M855 This cartridge has a 62-grain full metal jacket projectile, designed to offer better penetration against steel. It has a steel penetrator inside the projectile. This cartridge is identified by the green paint on the tip of the bullet, and is loaded to a pressure of 55,000 psi. M856 This cartridge is a tracer, ballistically matched to M855 ball ammunition. The bullet is very long due to a large load of tracer compound inside the bullet, but the OAL (overall length) of this cartridge is identical to other 5.56 NATO loads. The bullet is painted orange at the tip, and weighs in at 64 grains. M995 This cartridge has a 52-grain armor piercing projectile, composed of a tungsten inner core with steel sheath, lead filler and gilding metal jacket. The bullet is painted black at the tip. M996 This cartridge is a tracer, ballistically matched to M995 AP ammunition. The bullet is painted dim violet at the tip. Mk 255 mod 0 This cartridge has a 62-grain bullet, designed for reduced ricochet and limited penetration. It is marked by gray paint on the tip of the bullet. Mk 262 This cartridge has a 77-grain open-tip projectile. It shoots with a flatter trajectory and has a better terminal ballistic profile than most other 5.56 cartridges. This cartridge is loaded to a pressure of 58,700 psi. There are two variants of this cartridge: Mk 262 mod 0, which has no cannelure on the bullet, and Mk 262 mod 1, which does have the cannelure. Mk 318 mod 0 This cartridge has a 62-grain projectile. It fragments quite well on impact while retaining adequate penetration due to its design; it has an all-copper bullet with an open tip, and a solid body (allowing the rear part of the bullet to penetrate beyond the original wound, and through some barriers). Feed Systems This cartridge is generally fed through box magazines. In a light machine gun (LMG), this cartridge can also be fed from a belt. Category:Military cartridge